Steer-by-wire type steering apparatus

ABSTRACT

The present embodiments relate to a steer-by-wire type steering apparatus, which prevents a steering shaft from mechanically rotating by means of a gear structure when a driver turns the steering wheel at the maximum rotation angle or greater, so as to enable efficient limiting of the steering wheel operation of the driver to be within a maximum rotation angle without increasing the size, the weight and the like of a motor for transmitting torque to the steering shaft and the like, and to be advantageous with respect to production costs, packaging and the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2019-0056837, filed on May 15, 2019, which is hereby incorporated byreference for all purposes as if fully set forth herein. In addition, ifthis patent application claims priority for countries other than theUnited States for the same reason as above, all the contents areincorporated into this patent application by reference.

TECHNICAL FIELD

The present disclosure relates to a vehicle steering apparatus, and morespecifically, to a steer-by-wire type of steering apparatus that iscapable of effectively limiting the turning of a steering wheel within apredetermined rotation angle even without boosting the size and weightetc. of a motor that generates torque to be transferred to a steeringshaft by preventing the steering shaft from being rotated mechanicallyby a gear structure in a situation where the steering wheel is turnedover the predetermined rotation angle, and has advantages in terms ofcost, package, and the like.

BACKGROUND ART

A steer-by-wire type of steering apparatus (or referred to as asteer-by-wire steering system) is a type of electrical power assistedsteering apparatus, and is an apparatus capable of steering a vehicle byusing electrical power to steer a vehicle without a mechanicalconnection such as a steering column, a universal joint, and the likebetween a steering wheel and a front wheel steering apparatus.

That is, the turning of the steering wheel by a driver is converted intoan electrical signal and transferred to an electronic control unit(ECU), and the torque of an associated motor can be determined based onthe signal. In this case, since such a steer-by-wire steering systemdoes not have a mechanical connection, it is possible to reduce damageto the driver caused by mechanical components, and reduce the number ofhydraulic components and such mechanical connections. As a result of thereduction of the number of employed components, a vehicle weight can bereduced, and workload or process steps to be performed in amanufacturing assembly line can be reduced or simplified. In turn, fuelefficiency can be improved by reducing unnecessary energy consumptionfor steering the vehicle. Also, it is possible to achieve ideal steeringperformance by ECU programming.

However, since such a steer-by-wire type of steering system does nothave a mechanical connection between the steering shaft and wheels,weight feel caused by friction, jamming and the like of the wheels on aroad surface is not transferred to the driver, there is therefore aproblem in that steering feel is deteriorated. In particular, it isdesirable to provide an apparatus for preventing the steering wheel frombeing turned over a maximum rotation angle.

In a conventional steering system, a steering wheel has been designednot to be turned any more when the steering wheel reaches the maximumrotation angle by applying a torque in a direction opposite to adirection of turning the steering wheel by a driver using a motor forapplying the torque to a steering shaft. In this case, since the motorcapable of generating a high torque is required to offset steeringtorque provided by the driver, thus, there are disadvantages in terms ofcost, weight, package, and the like.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

To address these issues, embodiments of the present disclosure providesteer-by-wire type of steering apparatuses that are capable ofeffectively limiting the turning of a steering wheel within apredetermined rotation angle even without boosting the size and weightetc. of a motor that generates torque to be transferred to a steeringshaft by preventing the steering shaft from being rotated mechanicallyby a gear structure in a situation where the steering wheel is turnedover the predetermined rotation angle, and have advantages in terms ofcost, package, and the like.

Technical Solution

According to aspects of the present disclosure, a steer-by-wire type ofsteering apparatus is provided that includes a worm wheel coupled to asteering shaft and including a gear, and a worm shaft that is axiallyslidable, and includes a worm gear including a first worm gear port ionrotatable in a situation of engaging the gear and a second worm gearportion not rotatable in a situation of engaging the gear.

According to aspects of the present disclosure, a steer-by-wire type ofsteering apparatus is provided that includes a worm shaft including aworm gear formed on the outer circumferential surface thereof, and aworm wheel that is coupled to a steering shaft and includes a gearincluding a first gear portion rotatable in a situation of engaging theworm gear and a second gear portion not rotatable in a situation ofengaging the worm gear.

Effects of the Invention

According to embodiments of the present disclosure, it is possible toprovide steer-by-wire type of steering apparatuses that are capable ofeffectively limiting the turning of a steering wheel within apredetermined rotation angle even without boosting the size and weightetc. of a motor that generates torque to be transferred to a steeringshaft by preventing the steering shaft from being rotated mechanicallyby a gear structure in a situation where the steering wheel is turnedover the predetermined rotation angle, and have advantages in terms ofcost, package, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a portion of a steer-by-wiretype of steering apparatus according to aspects of the presentdisclosure.

FIG. 2 is a cross-sectional view of a structure in which components ofFIG. 1 are combined.

FIGS. 3 and 4 illustrate operating statuses in the structure of FIG.

FIGS. 5 to 7 are cross-sectional views of a portion of the steer-by-wiretype of steering apparatus according to aspects of the presentdisclosure.

FIG. 8 is a cross-sectional view of a portion of a steer-by-wire type ofsteering apparatus according to aspects of the present disclosure.

FIGS. 9 and 10 illustrate operating statuses in the apparatus of FIG.

FIG. 11 is a side view of a portion of the steer-by-wire type ofsteering apparatus according to aspects of the present disclosure.

FIGS. 12 and 13 are cross-sectional views of a portion of thesteer-by-wire type of steering apparatus according to aspects of thepresent disclosure.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description of examples or embodiments of the presentdisclosure, reference will be made to the accompanying drawings in whichit is shown by way of illustration specific examples or embodiments thatcan be implemented, and in which the same reference numerals and signscan be used to designate the same or like components even when they areshown in different accompanying drawings from one another. Further, inthe following description of examples or embodiments of the presentdisclosure, detailed descriptions of well-known functions and componentsincorporated herein will be omitted when it is determined that thedescription may make the subject matter in some embodiments of thepresent disclosure rather unclear. The terms such as “including”,“having”, “containing”, “constituting” “make up of”, and “formed of”used herein are generally intended to allow other components to be addedunless the terms are used with the term “only”. As used herein, singularforms are intended to include plural forms unless the context clearlyindicates otherwise.

Terms, such as “first”, “second”, “A”, “B”, “(A)”, or “(B)” may be usedherein to describe elements of the disclosure. Each of these terms isnot used to define essence, order, sequence, or number of elements etc.,but is used merely to distinguish the corresponding element from otherelements.

When it is mentioned that a first element “is connected or coupled to”,“contacts or overlaps” etc. a second element, it should be interpretedthat, not only can the first element “be directly connected or coupledto” or “directly contact or overlap” the second element, but a thirdelement can also be “interposed” between the first and second elements,or the first and second elements can “be connected or coupled to”,“contact or overlap”, etc. each other via a fourth element. Here, thesecond element may be included in at least one of two or more elementsthat “are connected or coupled to”, “contact or overlap”, etc. eachother.

When time relative terms, such as “after,” “subsequent to,” “next,”“before,” and the like, are used to describe processes or operations ofelements or configurations, or flows or steps in operating, processing,manufacturing methods, these terms may be used to describenon-consecutive or non-sequential processes or operations unless theterm “directly” or “immediately” is used together.

In addition, when any dimensions, relative sizes etc. are mentioned, itshould be considered that numerical values for an elements or features,or corresponding information (e.g., level, range, etc.) include atolerance or error range that may be caused by various factors (e.g.,process factors, internal or external impact, noise, etc.) even when arelevant description is not specified. Further, the term “may” fullyencompasses all the meanings of the term “can”.

Hereinafter, a steer-by-wire type of steering apparatus 100 according toaspects of the present disclosure is described with reference to FIGS. 1to 7.

The steer-by-wire type of steering apparatus 100 according to aspects ofthe present disclosure includes a worm wheel 120 coupled to a steeringshaft 110 and including a gear 121, and a worm shaft 130 that is axiallyslidable and includes a worm gear 131 including a first worm gearportion 131 a rotatable in a situation of engaging the gear 121 and asecond worm gear portion 131 b not rotatable in a situation of engagingthe gear 121.

The worm wheel 120 may be coupled to the steering shaft 110 connectedwith a steering wheel (not shown). The gear 121 may be formed on theouter circumferential surface of the worm wheel 120, and be engaged withthe worm gear 131 of the worm shaft 130.

The worm gear 131 engaged with the gear 121 may be formed on the outerperipheral surface of the worm shaft 130. Shaft portions 132 and 133 ofthe worm shaft 130 may be disposed on both sides of the worm gear 131.The shaft portion 132 disposed on one side of the worm shaft 130 may beconnected with a support member that is described below in furtherdetail, and the shaft portion 133 disposed on the other side thereof maybe connected with a motor (not shown) via a damping coupler (not shown).

That is, as the worm shaft 130 is rotated by the motor, resulting torquecan be transferred to the steering shaft 110 through the worm shaft 130and the worm wheel 120, and thereby the steering feel of a driver can beimproved.

The worm shaft 130 may be disposed to be axially slidable. That is, whenthe worm wheel 120 coupled to the steering shaft 110 is rotated by theturning of the steering wheel, the worm shaft 130 can axially slidetoward one side or the other side thereof based on the engagement of thegear 121 and the worm gear 131. That is, the worm shaft 130 can berotated by the motor and the worm wheel 120 and slide in the axialdirection.

The worm gear 131 of the worm shaft 130 may include the first worm gearportion 131 a rotatable in a situation of engaging the gear 121, and thesecond worm gear portion 131 b not rotatable in a situation of engagingthe gear 121.

Before the steering wheel reaches a predetermined rotation angle, forexample, a maximum rotation angle, the gear 121 engages the first wormgear portion 131 a, and as a rotation angle of the steering wheelincreases by the turning of a driver, the worm shaft 130 can axiallyslide. When the steering wheel reaches the maximum rotation angle, thegear 121 becomes engaged with the second worm gear portion 131 b, inthis situation, the worm wheel 120 and the steering shaft 110 cannotrotate any more, and thereby, it is possible to prevent the steeringwheel from being turned over the maximum rotation angle.

The gear teeth of the first worm gear portion 131 a and the gear teethof the second worm gear portion 131 b may have different shapes (e.g.,leads, pressure angles, pitch diameters, etc.), and the worm wheel 120can rotate in a situation where the gear 121 engages the first worm gearportion 131 a, and cannot rotate in a situation where the gear 121engages the second worm gear portion 131 b.

The shapes of the gear teeth of the first worm gear portion 131 a andthe second worm gear portion 131 b can be designed using a self-lockingcondition of the gear, which will be described below in more detail.

As described above, in the conventional steering system, the turning ofthe steering wheel by a driver over the maximum rotation angle has beenprevented by enabling torque resulting from the rotation of the wormshaft by a motor to be transferred to the worm wheel and the steeringshaft, and to do this, the motor capable of generating a high torque hasbeen required to offset steering torque provided by the driver. Thus,this can lead to disadvantages in terms of cost, weight, package, andthe like, In contrast, in the steer-by-wire type of steering apparatusaccording to aspects of the present disclosure, as the gear 121 becomesengaged with the second worm gear portion 131 b at the maximum rotationangle of the steering wheel, and thereby the worm wheel 120 is placed ina non-rotatable state, it is possible to effectively prevent thesteering wheel from being turned over the maximum rotation angle evenwithout boosting the size and weight etc. of the motor, and provideadvantages in terms of cost, package, and the like.

Referring to FIG. 2, the first worm gear portion 131 a may be disposedat a central portion of the worm gear 131, and the second worm gearportion 131 b may be disposed on both sides of the first worm gearportion 131 a.

Although FIGS. 2 to 4 show that the first worm gear portion 131 a andthe second worm gear portion 131 b have the same shape, these are merelyfor convenience of illustration. For example, as shown in FIGS. 5 to 7,it should be noted that the first worm gear portion 131 a and the secondworm gear portion 131 b may be formed differently in at least one of alead, a pressure angle, and a pitch diameter.

The first worm gear portion 131 a and the second worm gear portion 131 bmay be formed symmetrically about the center of the worm gear 131. Thatis, the center of the first worm gear portion 131 a may be aligned withthe center of the worm gear 131, and the second worm gear portion 131 bmay be formed to have an equal length from both sides of the first wormgear portion 131 a.

FIG. 2 shows a situation in which the center of the worm gear 131 isengaged with the gear 121 (hereinafter, referred to as “neutral status”for convenience), that is, the steering wheel is not rotated. FIGS. 3 to4 show situations in which as the worm shaft 130 slides, the second wormgear portion 131 b is engaged with the gear 121.

That is, when the steering wheel reaches a predetermined rotation angle,for example, the maximum rotation angle, as a driver turns the steeringwheel in the clockwise or counterclockwise direction, the gear 121becomes engaged with the second worm gear portion 131 b that is locatedon the right side in figures or the second worm gear portion 131 b thatis located on the left side in figures, by the sliding of the worm shaft130. Thereby, the turning of the steering wheel over the left or rightmaximum rotation angle can be effectively prevented.

In addition, bearings 141 and 142 for supporting the rotation of theworm shaft 130 may be disposed on the worm shaft 130, and the bearings141 and 142 may be disposed to be axially spaced apart from the wormgear 131.

As described above, the worm shaft 130 may include shaft portions 132and 133 disposed on both sides of the worm gear 131, and the bearings141 and 142 may be disposed to be spaced apart from the worm gear 131while being disposed on the shaft portions 132 and 133.

Although not shown in figures, the bearings 141 and 142 may be fixed inthe axial direction inside of a housing (not shown) to support therotation of the worm shaft 130, and the shaft portions 132 and 133 maybe disposed to be axially slidable in inner races of the bearings 141and 142.

As the bearings 141 and 142 are disposed on the shaft portions 132 and133 and disposed to be axially spaced apart from the worm gear 131, theworm shaft 130 can axially slide by distances between the bearings 141and 142 and ends of the worm gear 131.

In addition, as described above, in order for the worm shaft 130 to beconnected with the support member 160, the support member 160 may have aseating hole 161 that is axially opened, and the shaft portion 132 maybe inserted in the seating hole 161.

Further, an elastic member 150 may be disposed in the seating hole 161.The elastic member 150 can provide an elastic force when the worm shaft130 axially slides toward one side or the other side thereof from theneutral status, and enable the worm shaft 130 to easily return to theneutral status.

That is, both ends of the elastic member 150 in the axial direction maybe fixed to the worm shaft 130 and the support member 160 to provide theelastic force to the worm shaft 130 when compressed or stretched. Forexample, the ends of the elastic member 150 may be fixed to the wormshaft 130 and the support member 160 by welding or press fitting.

As shown in FIG. 3, when the worm shaft 130 slides leftward in thefigure, the elastic member 150 is compressed to provide an elastic forcerightward, and as shown in FIG. 4, when the worm shaft 130 slidesrightward in the figures, the elastic member 150 is stretched to providean elastic force leftward, so that the worm shaft 130 can be easilyreturned to its neutral status.

Since both ends of the elastic member 150 are fixed to the worm shaft130 and the support member 160, respectively, it is desirable for thesupport member 160 to rotate along with the worm shaft 130 so that theelastic member 150 can successfully provide the elastic force even whenthe worm shaft 130 rotates.

Accordingly, a first serration 134 may be formed on an outercircumferential surface of the shaft portion 132 of the worm shaft 130,and a second serration 162 coupled to the first serration 134 may beformed on an inner circumferential surface of the support member 160, asshown in FIG. 1.

As the first serration 134 and the second serration 162 engage eachother, when the worm shaft 130 axially slides, the shaft portion 132 canaxially slide in the seating hole 161, and when the worm shaft 130 isrotated by the motor, the support member 160 can be rotated together.

Although not shown in figures, a bush or bearing may be further disposedin the housing to support the rotation of the support member 160.

Meanwhile, as described above, the worm gear 131 has a structure ofincluding the first worm gear portion 131 a rotatable in a situation ofengaging the gear 121, and the second worm gear portion 131 b notrotatable in a situation of engaging the gear 121. Such a structure ofthe worm gear 131 can be designed considering the self-locking conditionof the gear.

A friction coefficient, a lead angle, and a pressure angle areconsidered for the self-locking condition of the gear. If theself-locking condition is satisfied, the gear cannot rotate even when anexternal force is applied, and if the self-locking condition is notsatisfied, the gear can rotate freely.

The self-locking condition of the gear is expressed by Equation 1 asfollows.

μ≥tan λ cos α  [Equation 1]

Here, μ denotes the friction coefficient between gear teeth, λ denotesthe lead angle, and α denotes the pressure angle.

The lead angle and the pressure angle denotes the lead angle and thepressure angle of the worm gear 131. In the case of the worm gear, thelead angle can be expressed by Equation 2 as follows.

$\begin{matrix}{{\tan\mspace{14mu}\lambda} = \frac{L}{\pi d}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, L denotes a lead, and d denotes a pitch diameter.

From Equations 1 and 2 above, the self-locking condition of the gear canbe derived as Equation 3 as follows.

$\begin{matrix}{µ \geq \frac{L\mspace{14mu}\cos\mspace{14mu}\alpha}{\; d}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Referring to Equation 3, the self-locking condition of the gear may, ormay not, be satisfied by changing the lead, pressure angle, or pitchdiameter. That is, the worm gear 131 may have a structure in which thefirst worm gear portion 131 a does not satisfy the self-lockingcondition, and the second worm gear portion 131 b satisfies theself-locking condition, and in this structure, in a situation where thefirst worm gear portion 131 a becomes engaged with the gear 121, theworm wheel 120 and the worm shaft 130 can rotate, and in a situationwhere the second worm gear portion 131 b becomes engaged with the gear121, the worm wheel 120 and the worm shaft 130 are not rotate.

That is, the second worm gear portion 131 b may have a small lead, asmall pressure angle, or a large pitch diameter compared with the firstworm gear portion 131 a, or may satisfy the self-locking condition bycomplying with two or more of these three conditions.

In some embodiments, referring to FIG. 5, the lead of the second wormgear portion 131 b may be smaller than the lead of the first worm gearportion 131 a.

Further, the lead of the second worm gear portion 131 b may be formed tobecome gradually smaller toward an axial edge.

That is, a lead L2 of the second worm gear portion 131 b at a locationspaced apart from the first worm gear portion 131 a may be smaller thana lead L1 thereof at a location close to the first worm gear portion 131a, and the leads L1 and L2 of the second worm gear portion 131 b may besmaller than the leads L0 of the first worm gear 131.

As the second worm gear portion 131 b is formed to become graduallysmaller toward an axial edge, when the gear 121 starts to engage thesecond worm gear portion 131 b, the steering feel of a driver graduallybecomes heavy, and in this situation, when the driver further turns thesteer wheel, the gear 121 becomes engaged with the second worm gearportion 131 b, thereby preventing the driver from operating the steeringwheel.

In some embodiments, referring to FIG. 6, the pressure angle of thesecond worm gear portion 131 b may be smaller than the pressure angle ofthe first worm gear portion 131 a.

Further, the pressure angle of the second worm gear portion 131 b may beformed to become gradually smaller toward the axial edge.

That is, a pressure angle α2 of the second worm gear portion 131 b at alocation spaced apart from the first worm gear portion 131 a may besmaller than a pressure angle α1 thereof at a location close to thefirst worm gear portion 131 a, and the pressure angles α1 and α2 of thesecond worm gear portion 131 b may be smaller than the pressure angle α0of the first worm gear 131.

Likewise, as the pressure angle of the second worm gear portion 131 b isformed to become gradually smaller toward the axial edge, when the gear121 starts to engage the second worm gear portion 131 b, the steeringfeel of a driver gradually becomes heavy, and in this situation, whenthe driver further turns the steer wheel, the gear 121 becomes engagedwith the second worm gear portion 131 b, thereby preventing the driverfrom operating the steering wheel.

In some embodiments, referring to FIG. 7, the pitch diameter of thesecond worm gear portion 131 b may be greater than the pitch diameter ofthe first worm gear portion 131 a.

Further, the pitch diameter of the second worm gear portion 131 b may beformed to become gradually greater toward the axial edge.

That is, a pitch diameter d2 of the second worm gear portion 131 b at alocation spaced apart from the first worm gear portion 131 a may begreater than a pitch diameter d1 thereof at a location close to thefirst worm gear portion 131 a, and the pitch diameters d1 and d2 of thesecond worm gear portion 131 b may be greater than the pitch diameter d0of the first worm gear 131.

Likewise, as the pitch diameter of the second worm gear portion 131 b isformed to become gradually greater toward the axial edge, when the gear121 starts to engage the second worm gear portion 131 b, the steeringfeel of a driver gradually becomes heavy, and in this situation, whenthe driver further turns the steer wheel, the gear 121 becomes engagedwith the second worm gear portion 131 b, thereby preventing the driverfrom operating the steering wheel.

Table 1 below shows a comparison of leads, pressure angles, and pitchdiameters of the first worm gear portion 131 a and the second worm gearportion 131 b.

TABLE 1

12 4 mm

15 5 deg

15 30 mm (L cosα)/πd 0.25 0.04 —

0.045 —

As shown in Table 1, in a situation where the second worm gear portion131 b is formed to have a lead and/or a pressure angle smaller than thefirst worm gear portion 131 a, and/or a pitch diameter greater than thefirst worm gear portion 131 a, as the first worm gear portion 131 a doesnot satisfy the self-locking condition, the first worm gear portion 131a can engage the gear 121 and freely rotate, and as the second worm gearportion 131 b satisfies the self-locking condition, the second worm gearportion 131 b cannot engage the gear 121 and rotate. Hereinafter, asteer-by-wire type of steering apparatus 800 according to aspects of thepresent disclosure will be described with reference to FIGS. 8 to 13.The steering apparatus of FIGS. 8 to 13 may have components equal, orsubstantially equal, to some components of the steering apparatusdescribed with reference to FIGS. 1 to 7. Such components may be labeledwith like reference numbers, the details of which may be replaced by thediscussions conducted above.

The steer-by-wire steering device 800 according to aspects of thepresent disclosure includes a worm shaft 830 including a worm gear 831,and a worm wheel 820 that is coupled to a steering shaft 810 andincludes a gear 821 including a first gear portion 821 a rotatable in asituation of engaging the worm gear 831 and a second gear portion 821 bnot rotatable in a situation of engaging the worm gear 831.

In a structure where the gear 821 of the worm wheel 820 includes thefirst gear portion 821 a and the second gear portion 821 b, before thesteering wheel reaches a predetermined rotation angle, for example, amaximum rotation angle, the worm gear 831 engages the first gear portion821 a. As the worm wheel 820 further rotates due to an increasedrotation angle of the steering wheel by the turning of a driver, whenthe steering wheel reaches the maximum rotation angle, the worm gear 831becomes engaged with the second gear portion 821 b, and the worm wheel820 and the steering shaft 810 cannot rotate any more. Thereby, it ispossible to prevent the steering wheel from being turned over themaximum rotation angle.

That is, the first gear portion 821 a can engage the worm gear 831 in astructure of not satisfying the self-locking condition, and the secondgear portion 821 b can engage the worm gear 831 in a structure ofsatisfying the self-locking condition.

Further, an area where the first gear portion 821 a is formed may have awider central angle than an area where the second gear portion 821 b isformed.

FIG. 8 shows a neutral status in which the center of the first gearportion 821 a engages the worm gear 831, and FIGS. 9 and 10 show stateswhere the second gear portion 821 b is engaged with the worm gear 831 bythe rotation of the worm wheel 820.

In the neutral status, since the worm gear 831 engages the center of thefirst gear portion 821 a, the second gear portion 821 b is placed at alocation opposite to the worm shaft 830.

Figures show an embodiment in which the first gear portion 821 a has acentral angle of about 270 degrees and the second gear portion 821 b hasa central angle of about 90 degrees.

In general, the steering wheel has a maximum rotation angle of about 540degrees in the clockwise or counterclockwise direction, and the wormwheel 820 is connected to the steering wheel through the steering shaft810 and can rotate by the same angle as the steering wheel. In order forthe worm gear 831 to engages the first gear port ion 821 a within themaximum rotation angle of the steering wheel, the rotation angle of theworm wheel 820 is needed to be reduced.

That is, in a situation where the maximum rotation angle of the steeringwheel is 180 degrees or more, the second gear portion 821 b becomesengaged with the worm gear 831 and the worm wheel 820 cannot rotatebefore the steering wheel reaches the maximum rotation angle. Therefore,the maximum rotation angle of the worm wheel 820 is needed to belimited.

In one embodiment, in a situation where the first gear portion 821 a hasa central angle of about 270 degrees, the steering wheel may have amaximum rotation angle of about 135 degrees in the clockwise orcounterclockwise direction. In this case, even though the maximumrotation angle of the steering wheel is limited, a steering angle ofwheels can be obtained by employing a separate gear structure, and adetailed description on such a structure is omitted.

Meanwhile, in another embodiment, by providing a gear structure betweenthe worm wheel 820 and the steering wheel, while maintaining the maximumrotation angle of the steering wheel, the worm wheel 820 can be designedto have a smaller rotation angle than the rotation angle of the steeringwheel, and thereby, it is possible to enable the second gear portion 821b to engage the worm gear 831 at the maximum rotation angle of thesteering wheel without reducing the steering feel of drivers.

Next, the second gear portion 821 b may have a lead angle, lead, and/orpressure angle smaller than the first gear portion 821 a, or may satisfythe self-locking condition by complying with two or more of these threeconditions.

In some embodiments, referring to FIG. 11, the lead angle of the secondgear port ion 821 b may be smaller than the lead angle of the first gearport ion 821 a.

Further, the lead angle of the second gear portion 821 b may be formedto become gradually smaller toward a center of the second gear portion821 b.

That is, a lead angle (λ2) of the second gear portion 821 b at thecenter of the second gear port ion 821 b may be smaller than a leadangle (λ1) thereof at a location close to the first gear portion 821 a,and the lead angles (λ1, λ2) of the second gear portion 821 b may besmaller than the lead angle (λ0) of the first gear portion 821 a.

As the second gear portion 821 b is formed to become gradually smallertoward the center of the second gear portion 821 b, when the worm gear831 starts to engage the second gear portion 821 b, the steering feel ofa driver gradually becomes heavy, and in this situation, when the driverfurther turns the steer wheel, the worm gear 831 becomes engaged withthe second gear portion 821 b, thereby preventing the driver fromoperating the steering wheel.

In some embodiments, referring to FIG. 12, the lead of the second gearportion 821 b may be smaller than the lead of the first gear portion 821a.

Further, the lead of the second gear portion 821 b may be formed tobecome gradually smaller toward the center of the second gear portion821 b.

That is, a lead L2′ of the second gear portion 821 b at the center ofthe second gear portion 821 b may be smaller than a lead L1′ thereof ata location close to the first gear portion 821 a, and the leads L1′ andL2′ of the second gear portion 821 b may be smaller than the lead L0′ ofthe first gear portion 821 a.

Likewise, as the second gear portion 821 b is formed to become graduallysmaller toward the center of the second gear portion 821 b, when theworm gear 831 starts to engage the second gear portion 821 b, thesteering feel of a driver gradually becomes heavy, and in thissituation, when the driver further turns the steer wheel, the worm gear831 becomes engaged with the second gear portion 821 b, therebypreventing the driver from operating the steering wheel.

In some embodiments, referring to FIG. 13, the pressure angle of thesecond gear portion 821 b may be smaller than the pressure angle of thefirst gear portion 821 a.

Further, the pressure angle of the second gear portion 821 b may beformed to become gradually smaller toward the center of the second gearportion 821 b.

That is, a pressure angle (α2′) of the second gear portion 821 b at thecenter of the second gear portion 821 b may be smaller than a pressureangle (α1′) thereof at a location close to the first gear portion 821 a,and the pressure angles (α1′, α2′) of the second gear port ion 821 b maybe smaller than the pressure angle (α0′) of the first gear portion 821a.

Likewise, as the second gear portion 821 b is formed to become graduallysmaller toward the center of the second gear portion 821 b, when theworm gear 831 starts to engage the second gear portion 821 b, thesteering feel of a driver gradually becomes heavy, and in thissituation, when the driver further turns the steer wheel, the worm gear831 becomes engaged with the second gear portion 821 b, therebypreventing the driver from operating the steering wheel.

Further, in a situation where the second gear portion 821 b is formed tohave a lead angle, lead, and/or pressure angle smaller than the firstgear portion 821 a, as the first gear portion 821 a does not satisfy theself-locking condition, the first worm gear portion 821 a can engage theworm gear 831 and freely rotate, and as the second gear portion 821 bsatisfies the self-locking condition, the second gear portion 821 bcannot engage the worm gear 831 and rotate.

Further, as not shown in figures, embodiments of the present disclosuremay have not only a structure in which the gear 821 of the worm wheel820 includes the first gear portion 821 a and the second gear portion821 b, but also a structure in which the worm gear 831 of the worm shaft831 includes a first worm gear portion rotatable in a situation ofengaging the gear 821 and a second worm gear portion not rotatable in asituation of engaging the gear 821, as shown in FIGS. 1 to 7.

In such a case, the worm shaft 830 may further include a bearing, anelastic member, a support member, and the like coupled to, and spacedapart from, the worm gear 831 so that the worm shaft 830 can axiallyslide.

In the steer-by-wire type of steering apparatus having the structuresdescribed above, it is possible to effectively limit the turning of thesteering wheel within a predetermined rotation angle even withoutboosting the size and weight etc. of a motor that generates torque to betransferred to the steering shaft by preventing the steering shaft frombeing rotated mechanically by a gear structure in a situation where thesteering wheel is turned over the predetermined rotation angle, andprovide advantages in terms of cost, package, and the like.

The above description has been presented to enable any person skilled inthe art to make and use the technical idea of the present disclosure,and has been provided in the context of a particular application and itsrequirements. Various modifications, additions and substitutions to thedescribed embodiments will be readily apparent to those skilled in theart, and the general principles defined herein may be applied to otherembodiments and applications without departing from the spirit and scopeof the present disclosure. The above description and the accompanyingdrawings provide an example of the technical idea of the presentdisclosure for illustrative purposes only. That is, the disclosedembodiments are intended to illustrate the scope of the technical ideaof the present disclosure. Thus, the scope of the present disclosure isnot limited to the embodiments shown, but is to be accorded the widestscope consistent with the claims. The scope of protect ion of thepresent disclosure should be construed based on the following claims,and all technical ideas within the scope of equivalents thereof shouldbe construed as being included within the scope of the presentdisclosure.

What is claimed is:
 1. A steer-by-wire type of steering apparatuscomprising: a worm wheel coupled to a steering shaft and including agear; and a worm shaft that is axially slidable, and include a worm gearincluding a first worm gear portion rotatable in a situation of engagingthe gear and a second worm gear portion not rotatable in a situation ofengaging the gear.
 2. The steer-by-wire type of steering apparatusaccording to claim 1, wherein the first worm gear portion is disposed ata central portion of the worm gear, and the second worm gear portion isdisposed on both sides of the first worm gear portion.
 3. Thesteer-by-wire type of steering apparatus according to claim 1, whereinat least one bearing for supporting rotation of the worm shaft iscoupled to the worm shaft, and the at least one bearing is disposed tobe axially spaced apart from the worm gear.
 4. The steer-by-wire type ofsteering apparatus according to claim 1, wherein an edge of the wormshaft is inserted in a support member having a seating hole that isaxially opened, and an elastic member supported by the support memberand elastically supporting the worm shaft is disposed in the seatinghole.
 5. The steer-by-wire type of steering apparatus according to claim4, wherein a first serration is formed on an outer circumferentialsurface of the edge of the worm shaft, and a second serration coupled tothe first serration is formed on an inner circumferential surface of thesupport member.
 6. The steer-by-wire type of steering apparatusaccording to claim 1, wherein a lead of the second worm gear portion issmaller than a lead of the first worm gear portion.
 7. The steer-by-wiretype of steering apparatus according to claim 6, wherein the lead of thesecond worm gear portion gradually becomes smaller toward an axial edge.8. The steer-by-wire type of steering apparatus according to claim 1,wherein a pressure angle of the second worm gear portion is smaller thana pressure angle of the first worm gear portion.
 9. The steer-by-wiretype of steering apparatus according to claim 8, wherein the pressureangle of the second worm gear portion gradually becomes smaller towardan axial edge.
 10. The steer-by-wire type of steering apparatusaccording to claim 1, wherein a pitch diameter of the second worm gearportion is greater than a pitch diameter of the first worm gear portion.11. The steer-by-wire type of steering apparatus according to claim 10,wherein the pitch diameter of the second worm gear portion graduallybecomes greater toward an axial edge.
 12. A steer-by-wire type ofsteering apparatus comprising: a worm shaft including a worm gear; and aworm wheel coupled to a steering wheel, and including a gear including afirst gear portion rotatable in a situation of engaging the worm gearand a second gear portion not rotatable in a situation of engaging theworm gear.
 13. The steer-by-wire type of steering apparatus according toclaim 12, wherein an area where the first gear portion is formed has awider central angle than an area where the second gear portion isformed.
 14. The steer-by-wire type of steering apparatus according toclaim 12, wherein a lead angle of the second gear portion is smallerthan a lead angle of the first gear portion.
 15. The steer-by-wire typeof steering apparatus according to claim 14, wherein the lead angle ofthe second gear portion gradually becomes smaller toward a center of thesecond gear portion.
 16. The steer-by-wire type of steering apparatusaccording to claim 12, wherein a lead of the second gear portion issmaller than a lead of the first gear portion.
 17. The steer-by-wiretype of steering apparatus according to claim 16, wherein the lead ofthe second gear portion gradually becomes smaller toward a center of thesecond gear portion.
 18. The steer-by-wire type of steering apparatusaccording to claim 12, wherein a pressure angle of the second gearportion is smaller than a pressure angle of the first gear portion. 19.The steer-by-wire type of steering apparatus according to claim 18,wherein the pressure angle of the second gear portion gradually becomessmaller toward a center of the second gear portion.